The invention relates to valves used in controlling the flow of fluids in a fluidic system and, more particularly, to a valve and components thereof suitable for use in high temperature, corrosive, abrasive, and other hostile environments.
Valves are commonly employed as flow control devices in all types of fluidic systems. These valves may have many different configurations, depending on the particular application, such as a ball valve, a gate valve, a globe valve, a slide valve, a check valve and the like. Such valves typically comprise a housing having a fluid inlet and a fluid outlet, a flow-control element disposed within the housing between the inlet and the outlet, and one or more seals engaging the flow-control element to prevent the fluid from flowing between the housing and the flow-control element and/or out of the housing. The valves often also include one or more biasing devices, typically metal coil springs, for urging the flow-control element and seals toward each other. In addition, valves that are used for providing on-off and/or flow-rate regulation functions generally also include an actuating device for moving the flow-control element between an open position, where flow of the fluid between the inlet and the outlet is permitted, and a closed position in which the fluid is not able to flow between the inlet and the outlet. The actuating device can be manually operated or can be coupled with an electrical, hydraulic, or pneumatic actuator that operates the actuating device in response to signals from a controller connected with the actuator.
In valves as described above, the various components of the valve are generally comprised of materials appropriate for the particular application. For example, many components for a low-pressure cold water valve can be comprised of a polymer material, whereas a valve used at higher pressures and temperatures may be comprised predominantly of metallic components. However, common valves generally become unsuitable as the temperature and the hostility of the environment increases. For instance, where corrosive and/or abrasive-containing fluids are being handled, commonplace valves may be easily damaged unless special measures are taken in the design of the valve and/or the remainder of the fluidic system to protect the valves. Without costly measures to allow the use of commonplace valves in hostile environments, a serious safety hazard or reliability problem may be created. As an example of such measures, high-temperature fluidic processes may require hot process fluids to be cooled before being pumped or piped through a valve to a subsequent location where the fluid may again have to be restored to the proper operating temperature for the process, thereby reducing the efficiency and raising the cost of such an operation. Thus, there exists a need for a valve capable of operating safely, reliably, and economically in high temperature or other hostile environments, such as in fluidic systems where corrosive and/or abrasive-containing fluids are present.
Still further concerns exist with common valves in emergency situations where the temperatures of the fluids to which the valves are exposed are not controllable. For example, in the event of a fire at a petrochemical refinery, excessive temperatures may cause common valves to fail, thereby allowing storage tanks to deleteriously feed the fire with catastrophic results. At excessively high temperatures, seals internal to the valve may fail, the seat and/or the flow-control element may warp, and/or any springs present within the valve may lose their spring constants and thereby allow separation of the components biased by the spring. Thus, the endeavor to develop a valve suitable for use at excessively high temperatures has led to the proposal that ceramic materials could be used for valve fabrication. See, for example, U.S. Pat. No. 4,372,531 to Rollins et al.
Ceramics are generally recognized as a class of refractory materials suitable for use in high temperature applications and in corrosive or abrasive environments. However, most ceramics are typically deficient in their ability to withstand tensile stresses without failure. Therefore, where components are fabricated from ceramic materials, these components are configured and utilized such that they are exposed mainly to compressive stresses and little or no tensile stresses. However, many components of a valve may experience significant tensile stresses caused, at least in part, by shear stresses imparted by the fluid and possibly the configuration and utilization of the component. Thus, where ceramic has been utilized in the fabrication of valve components, additional measures must often be taken to assure that the valve functions as intended without the ceramic components failing. Generally, these additional measures comprise supplemental components fabricated of a material more appropriate for withstanding tensile stresses, but typically not as able to withstand excessively high temperatures as the ceramic material. For instance, a Teflon seal may be placed between the flow-control element and the seat. This results in a valve where the critical and/or fluid-contacting components are not entirely able to withstand excessively high temperature or other hostile environments to which the valve may be exposed. Thus, there exists a further need for a valve capable of withstanding high temperature or other hostile environments, wherein the critical and/or fluid-contacting components are fabricated of refractory materials such as a ceramic.
Thus, a continued need exists for a practical valve capable of withstanding excessively high temperatures or other hostile environments, wherein the valve is relatively simple to produce, reliable, and cost effective.
The above and other needs are met by the invention which, in one embodiment, provides a flow-controlling device or valve for controlling the flow of a fluid and capable of withstanding extreme temperatures of over 600xc2x0 C. and also capable of withstanding abrasive and corrosive environments. In accordance with the invention, all of the biasing and sealing components in the valve, including the flow-control element, the seat sealingly engaging the flow-control element, and the spring for biasing the seat into sealing contact with the flow-control element, are prepared from highly stable refractory and/or toughened ceramic materials that are capable of withstanding abrasives, corrosives, and extreme temperatures. Preferably, no elements made of polymer materials such as rubber or rubber-like polymers, plastic materials such as TEFLON, or the like, are included in the valve. The valve components are simple in design and can be retrofitted into existing standard valve housings, including, but not limited to, poppet and ball valves. These valves can withstand process fluids at over 500xc2x0 C., at over 640xc2x0 C., and at red-hot conditions of 1000xc2x0 C. or more over extended periods of time comparable to prior designs that have current practical limits of about 200 to 400xc2x0 C.
Certain refractory and/or toughened ceramics materials, commonly referred to as advanced ceramics, exhibit useful resistance to tensile stress when the material is heat treated in a certain manner. More particularly, a yttria-stabilized zirconia or other comparable ceramic material that is fully annealed so that porosity in the material is minimized and so that the material is substantially homogenous, is capable of substantial elongation and compression without failure. This flexible ceramic allows the fabrication of fluid-contacting, sealing, or other valve members from the same heat- and wear-resistant materials.
The valve in accordance with one preferred embodiment of the invention comprises a housing having a flow passage formed therethrough, a flow-control element disposed within the flow passage of the housing, at least one seat, and a biasing device urging the seat and the flow-control element relatively toward each other. The housing passage has an inlet adapted to receive the fluid and an outlet through which the fluid is discharged. The flow-control element is disposed in the passage between the inlet and the outlet and acts in conjunction with the seat to control the flow of the fluid therethrough. Each of the flow-control element, the seat, and the biasing device are comprised of refractory and/or toughened materials including, for example, an advanced ceramic. More specifically, the seat, the flow-control element, the biasing device, or other components may be advantageously fabricated of a flexible ceramic material. In some embodiments, the seat and the biasing device are prepared as a unitary structure from a toughened ceramic, including, for example, yttria-stabilized zirconia and others. The flow-control element can be prepared from a harder ceramic, if desired. The valve in some embodiments of the invention further comprises an actuating device operably engaging the flow-control element for moving the flow-control element between closed and open positions, and for varying the degree of flow restriction by the flow-control element in some cases. If desired, the actuating device can also be prepared from the same types of materials as the flow-controlling element, the seat, and the biasing device.
In an alternative embodiment, the valve may further comprise a shield operably engaging the seat and adapted to channel the fluid through the valve passage such that the shield prevents fluid flowing through the valve from contacting the biasing device. This embodiment can be useful if it is desired to preclude abrasive particles in the fluid from contacting the biasing device. However, it normally should not be necessary to isolate a ceramic spring from abrasives that may be contained in a process fluid. Of course, if the valve were operated at lower temperatures such that a spring made from a more-conventional material such as steel were employed, then it may be advantageous to shield the spring from abrasives. If desired, the seat and the shield can be integrally fabricated from a unitary piece of ceramic material; furthermore, the seat, the biasing device, and the shield can be integrally fabricated from a unitary piece of ceramic material. In some embodiments of the invention such as relief or safety valves that open in response to fluid pressure differential across the flow-control element, the flow-control element and the biasing device can be integrally fabricated from a unitary piece of ceramic material.
In one embodiment of the invention, the valve comprises a ball valve for controlling the flow of a fluid. Generally, the ball valve comprises a housing, a valve ball disposed within the housing, at least two seats operably engaging the valve ball, a biasing device operably engaging each seat, optionally a shield operably engaging each seat, and a valve stem operably engaging the valve ball. The housing defines an inlet adapted to receive the fluid and an outlet adapted to dispense the fluid, and the valve ball is disposed between the inlet and the outlet and defines a bore capable of establishing communication between the inlet and the outlet. The seat is adapted to prevent the fluid from flowing between the housing and the valve ball, while the biasing device operably engages the seat and urges the seat into sealing engagement with the valve ball. The shield, when present, extends from the valve ball to at least one of the inlet and the outlet and is adapted to channel the fluid therebetween. The valve stem operably engages the valve ball and is capable of actuating the valve ball between an open position in which the fluid is capable of flowing between the inlet and the outlet through the bore in the valve ball and a closed position in which the fluid is not capable of flowing between the inlet and the outlet through the bore in the valve ball. The valve ball, the seat, the biasing device, and the shield, if included, are comprised of a refractory material such as ceramic, and at least the biasing device is formed of a toughened refractory material that is flexible. In one particularly advantageous embodiment, the seat, the biasing device, and the shield, if present, are an integral structure fabricated from a unitary piece of a ceramic material such as, for example, yttria-stabilized zirconia.
In another embodiment of the invention, the valve comprises a fluid-operated valve in which the flow-control element is not actuated from outside the valve but rather is moved between open and closed positions by fluid pressure differential across the flow-control element. Examples of such valves include non-return or check valves, relief valves, and safety valves. The valve generally comprises a housing having a passage extending therethrough from an inlet to an outlet of the housing, a seat disposed in the housing, a flow-control element such as a ball or poppet disposed in the passage of the housing such that the flow-control element is movable between an open position spaced from the seat such that fluid can flow through the valve between the seat and the flow-control element and a closed position engaging the seat so as to prevent fluid flow through the valve, and at least one biasing device for urging the flow-control element relatively toward the seat. In accordance with the invention, the seat, flow-control element, and each biasing device are all formed from a refractory material and at least the biasing device is formed of a toughened refractory material. In one embodiment, the flow-control element comprises a poppet and can be integrally fabricated with a biasing device from a single unitary piece of toughened ceramic material. Additionally or alternatively, the seat and a biasing device can be integrally fabricated from a single unitary piece of toughened ceramic material.
The invention also encompasses a method of fabricating a sealing device for interacting with a flow-control element of a valve for controlling the flow of a fluid. In accordance with the invention, a bore is formed in a cylinder of a refractory material such that the bore defines an axis and is adapted to cooperate with the flow-control element to control the flow of a fluid through the bore. In some instances, the sealing device may be fabricated starting with a tubular member having appropriate inner and outer diameters, such that the bore is already present. A seating surface is then formed in the cylinder generally perpendicular to the axis of the bore. A cylindrical channel is then formed in the cylinder such that the channel extends into the cylinder concentrically with the bore and thereby forms a cylindrical spring blank outward of the channel and a cylindrical spring shield inward of the channel such that the inner surface of the spring shield defines the bore. The spring blank is then machined along a generally helical or spiral path so as to fabricate a biasing device in the form of a helical spring. In this manner, the sealing device is formed as an integral structure from a unitary piece of a refractory material, such as a flexible ceramic, where the biasing device is capable of biasing the seat into sealing engagement with the flow-control element and the spring shield channels the fluid flow such that contact of the fluid with the biasing device and/or the housing is avoided.
Still another advantageous aspect of the invention comprises a device for sealing an actuator that is operably connected to a flow-control element disposed within a main housing of a valve for controlling the flow of a fluid. Generally, the device comprises an actuator housing adapted to engage the main housing so as to surround the actuator, a compliant packing adapted to be disposed about the actuator, an end cap operably engaging the actuator housing, and a biasing device disposed within the actuator housing intermediate the end cap and the packing. The actuator housing has a proximal end adjacent to the flow-control element and an opposing threaded distal end. The packing is disposed about the actuator at the proximal end of the actuator housing adjacent to the flow-control element to form a seal between the actuator and the actuator housing. The end cap is secured to the threaded end of the actuator housing and is generally adapted to allow the actuator to pass therethrough. The biasing device is configured such that a substantially uniform compressive force is applied to the packing about the actuator when the biasing device interacts with the end cap and the packing. The packing is thereby compressed between the actuator housing and the actuator to form a seal therebetween. The packing can be comprised of, for example, a graphite-impregnated foil material or a graphite-impregnated ceramic fiber. The actuator and biasing device can be prepared from ceramic materials of the same type as is used in the other components, if desired.
Thus, the invention provides fluid-contacting and other components of a valve that are sufficiently flexible and generally heat- and wear-resistant and can withstand significant applied tensile stresses. Certain components may be fabricated as unitary structures, thereby reducing the number of components required for the valve assembly. Embodiments of the invention therefore provide a valve capable of operating in high temperature and other hostile environments in a relatively safe and reliable manner, while the characteristics of the ceramic material facilitate cost-effective fabrication techniques. It will be recognized, therefore, that the invention facilitates the achievement of a number of distinct advantages over prior art valves used in high-temperature or other hostile environments.